1. Field of the Invention
The present invention relates to a dipole coil, more particularly to a saddle shaped dipole coil for use in a synchrotron radiation ray generating device (so called a SOR ring) and particle accelerating accumulator or the like.
2. Description of the Prior Art
As shown in FIG. 1, in order to accelerate movement of charged particles or to polarize the progress direction of the particles such as ion or electron projected in a duct 3, there are provided a pair of elongated ring shaped upper and lower coil layers 51 and 52 opposing each other arranged on the upper and lower surfaces of the duct 3 respectively elongated in the longitudinal direction of the duct 3, thereby forming a saddle type dipole coil.
By applying electric current flowing through the upper and lower coils 51 and 52 of the saddle type dipole coil constituted as mentioned above, there occurs a magnetic field with fundamental bipolar components naturally caused by the current flowing through the upper and lower coils 51 and 52 and, in addition, there occurs a magnetic field with quadrapole, sextapole, . . . and 2n-pole components, wherein the number 2n of the poles is determined depending on the positioning relation between the upper and lower coils 51 and 52 in the lateral cross section of the duct 3. Among these multi-pole components of the magnetic field as mentioned above, the bipolar and quadrupole components of the magnetic field are indispensable for forming a particle accelerator. However, the components of sextupole or more than six multi-pole affect an undesired disturbance on the movement of the charged particles running through the duct 3.
Therefore, in the prior art, the conventional saddle type dipole coil is so designed that the integral value of the multi-pole components of the magnetic field is minimized with respect to the entire longitudinal portion of the dipole coil. In addition, the integral value .intg.(.DELTA.B/B)(dl/l) of the multi-pole components of the magnetic field must be reduced approximately 10.sup.-4. Herein, B represents the strength of the magnetic field at the center portion thereof, .DELTA.B denotes a difference between the strength at the center portion thereof and the strength of the magnetic field in the peripheral portion shifted from the center portion, and l denotes a length of the coil in the longitudinal direction thereof.
As described above, in order to minimize the amount of the integral values of the multi-pole components when the upper and lower coils 51 and 52 are arranged on the duct 3 to form a saddle type dipole coil, the degree of freedom for setting the coils 51 and 52 on the duct 3 must be set large to some degree when the upper and lower coils 51 and 52 are designed. Moreover, in order to situate the upper and lower coils 51 and 52 on the predetermined positions of the duct 3 to minimize the integral values of the sextapole or more than six multi-pole components of the magnetic field mentioned above, there must be considered such cases that, it is required to provide a lot of insulation spacers between the coil conductors formed of a set of series-connected turns, and that the number of the laminated layers provided with coil conductors is so increased as to eliminate the multi-pole components in order to minimize the integral values of the multi-pole components. Moreover, a distance "a" between the rising portion and the end portion of the respective coils 51 and 52 must be set in various suitable values as shown in FIG. 1.
As mentioned above, in the conventional saddle type dipole coil, there has been a problem that it is very troublesome and difficult to design and make such a dipole coil.